It may be interesting to look at in some forms, but mold is the bane of a building manager’s or cultivator’s existence. It makes spaces designed for people uninhabitable and when it shows up in an indoor agriculture facility it can mean that an entire crop must be destroyed. Unfortunately, mold mitigation is difficult and expensive.
For the last 20 years there has been a great deal of research into mold by professional engineering associations. Founded in 1894 the American Society of Heating Refrigeration and Air Conditioning Engineers (ASHRAE) has well over 50,000 members. The gold standard in the climate control business are peer-reviewed publications from ASHRAE. I accept ASHRAE’s conclusions on any subject as gospel and I believe you will come to the same conclusion.
When it comes to mold, the results have been in for some time. It turns out there is no magic bullet. Like a chronic disease; you can control it, but you cannot cure it. Here is what the experts tell us about some of the ways people are trying to control mold.
Why does mold grow?
The results are definitive, and the action taken to prevent mold is clear.
Mold needs four things to exist and these four things are arranged in what they refer to the mold square. Break one side of the square and you can control mold. Let’s look more closely at each side of the square.
1) Food Source: mold eats anything organic. Mold has been know to grow on glass. Not because it eats glass but because the glass was dirty and the mold found something in the dirt it could eat. Keep your rooms clean but otherwise forget about starving out the mold. Ain’t gonna happen.
2) Mold Spores: Mold spores are everywhere. Most of them come in from outdoors but they stick to our shoes and clothing and anything else brought in from outdoors. The way to minimize mold spores is to minimize these sources. Outdoor air is the worst. There are other steps you could take but the most effective is to minimize or eliminate outdoor air. If you must bring in outdoor air it must be filtered through a filter with a minimum efficiency of MERV-8. The filters need to fit tightly in the filter housing so that air, and mold spores can’t sneak around the edges of the filters or the housing.
3) Temperature: The temperature you need is the temperature you need. Not much you can do about that but if a little change of the temperature will reduce mold and not impact the crop you may want to consider it.
4) Moisture: Moisture comes in two forms 1) open water like puddles and 2) humidity in the air. Humidity is what you should be most concerned with. Different strains of mold thrive at different humidity levels. A good guideline: keep the relative humidity below 60% at all times. Many varieties of mold thrive at 60% RH and above. That 60% is the RH at the plants’ leafs and flowers.Your humidity sensor may likely be across the room or in a dehumidifier. It is vital that air be circulated through and around the leaves and flowers at all times to make sure the local humidity there is no higher than the humidity seen at the sensors. To be safe I would bump the humidity setting at the sensor down to 55% to give yourself a little safety factor at the flower.
Do Ultra Violet Lights Help?
ASHRAE has a whole chapter devoted to Ultra Violet (UV) lights in its Humidity Control Design Guide on HVAC systems and equipment. In general, when properly applied, ultra violet lights have different levels of effectiveness at inactivating bacteria and fungal spores.
• UV lights are most effective against bacteria like the ones that cause staph infections, and do a decent job on bacteria like the ones that cause tuberculosis.
• They have some effect on bacteria like the one that causes anthrax.
• At the very bottom of the list; UV lights are good at inactivating fungal spores (mold).
The published data indicates: the less effective UV lights are against something, the more concentrated the light needs to be, and the longer the organism must be exposed to it. Unfortunately, there is a significant lack of data that explains how much exposure you need to kill a mold spore. I found well researched papers on the effectiveness against bacteria, but nothing on mold. As near as I can tell, ASHRAE is silent on that topic.
UV lights consume power and generate heat. Just like all the other lights in the building, they add to the cost of running your air conditioning. Here are some quick calculations that will get you into the ballpark of what that really costs you. If your building needs 100 tons of air conditioning, adding UV lights means you must buy an additional 2 tons to cool the added heat load from the lights. If you have 100 tons of air conditioning with UV lights and you pay $0.10 per kW of electricity, your rough cost to operate the air conditioning 24/7/365 is about $110,000. Add the cost to operate the UV lights and the additional air conditioning to cool them and that cost goes up about $10,000 more.
Finally, light bulbs burn out. If UV lights are installed inside ducts or air conditioning units you need a method to tell you when the bulbs burn out. You can’t just open the unit and look at them because safety regulations require a switch that turns the lights off when the unit is opened. ASHRAE recommends that a window be added so people can look at the lights in operation, but the window rarely gets installed in the real world. As a result, a lot of UV light bulbs don’t get changed when they burn out.
Conclusion: UV lights are good for controlling bacteria. Mold? Not proven.
Control Mold with Environmental Control Equipment
One of the first environmental control go-to’s is a dehumidifier. The mechanics of a dehumidifier is pretty straight forward and they all work pretty well. But, keep in mind that understanding the relationship between a dehumidifier’s controls and a sensor is very important. The humidity control from a dehumidifier is only as good as the sensor used to detect it.
When dehumidifiers are mass-produced for the retail market, the first place manufacturers scrimp is in on the sensor. You can buy sensors for $5. Yes, they are slow and inaccurate, and they are designed for use in a factory, not a laboratory. If the dehumidifier is rated in pints per day, my professional experience tells me that it has a sensor that is no more 5% plus or minus accurate. That means that if you look at the display on the dehumidifier and it says it is 55% — the actual humidity measured by the highest quality sensor may really be 60% RH or it might be 50%. You just don’t know.
When it comes to sensors — you get what you pay for. If you want an accurate sensor that reacts quickly to changes in RH, the more expensive it will be. But again, you get what you pay for. More expensive humidity sensors provide more accuracy — within 1% of the actual number. That means: if you’re seeing the display at 50% — the real humidity measured by the highest quality sensor may be between 49% to 51%. That small difference is most likely something you can live with.
Learning to control the environment in which mold can live is your best chance at keeping mold from taking over your facility. So investigating proven systems designed to control mold through the temperature and humidity in data centers or an indoor agriculture will help you prevent unwanted moisture from condensing on surfaces within your facility.